vfs: strengthen checking of file range inputs to generic_remap_checks

File range remapping, if allowed to run past the destination file's EOF,
is an optimization on a regular file write.  Regular file writes that
extend the file length are subject to various constraints which are not
checked by range cloning.

This is a correctness problem because we're never allowed to touch
ranges that the page cache can't support (s_maxbytes); we're not
supposed to deal with large offsets (MAX_NON_LFS) if O_LARGEFILE isn't
set; and we must obey resource limits (RLIMIT_FSIZE).

Therefore, add these checks to the new generic_remap_checks function so
that we curtail unexpected behavior.

Signed-off-by: Darrick J. Wong <[email protected]>
Reviewed-by: Amir Goldstein <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Dave Chinner <[email protected]>

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